This invention relates to remote copy in computer systems.
In recent years, the operations of companies and other organizations have come to depend on computer systems, and data managed by such computer systems is gaining its importance. As a result, storage systems where data is stored are demanded to have availability high enough to keep the systems running without losing data in the event of a system failure, disasters, or the like.
One measure proposed to answer the demand is the remote copy technology in which two or more storage systems connected to one another store the same data. According to the remote copy technology, when data is updated in a volume of one of storage systems, the updated data is copied to another of the storage systems that is connected to this storage system. This makes a data update in one volume destaged to another volume, ensuring the consistency of data stored in these volumes. Therefore, in the case where one volume is put out of use by a system failure or disasters, a data loss or shutdown of the system can be avoided by using another volume.
The early connection form (topology) of remote copy has been a simple one composed of only two volumes with one acting as a copy source and the other as a copy target. Topologies that have been proposed lately are more complicated, and some of them are composed of three or more volumes in order to achieve higher availability. Typical examples of such topologies are multi target topologies and cascading topologies. A multi target topology is a form in which one copy source volume is paired with plural copy target volumes (see JP 2003-122509 A, for example). Here, the term pair refers to a combination of a copy source volume and a copy target volume. A cascading topology is a form in which plural pairs are linked in series (see U.S. Pat. No. 6,209,002, for example). It is also possible to combine a multi target topology and a cascading topology to build an even more complicated topology.